Method for producing vapor permeable polyurethane fibers



27, 1970 T. SCHACHOWSKOY 3,536,639

METHOD FOR PRODUCING VAPOR PERMEABLE POLYURETHANE FIBERS Filed April 21,1966 IO 0 70 OM50 90 I00 9'0 THF IN VENTOR THEODOR SCHACHOWSKOY ATTORNEYS.

United States Patent C) F Int. Cl. B29d 7/20, 27/ 4; C08g 22/10, 53/ 08;D0611 3/08 US. Cl. 260-25 6 Claims ABSTRACT OF THE DISCLOSURE Productionof air and water-vapor-permeable films of polyurethane by coagulatingpolyurethane from a mixture of dimethylsulfoxide and tetrahydrofuran,dioxane, acetone or methyl-ethyl ketone.

This invention relates to the production of sheet or film-form materialshaving a relatively high degree of air and water vapor permeability. Itmore particularly refers to the production of an air and water vaporpermeable coating on a substrate.

Luggage, upholstery material or other non-apparel goods have been madefrom plastic materials which have the appearance and hand of leather formany years. The production of artificial leather for these uses is arecognized art which is relatively highly developed and which has beenrelatively successful.

Attempts have been made for many years to produce artificial leather forapparel use with only limited success at best. The primary problemfacing the art is producing artificial or synthetic leather for appareluse is and has been the difficulty of producing a self-supporting sheetor film-form material which not only has the look and hand of leather,but also has the breathing qualities of leather, i.e., the ability topass water vapor and air and yet be relatively impervious to liquidwater. Additionally, particularly in the case of shoe upper material,the synthetic leather product must be relatively soft and supple suchthat it is resistant to creasing and paper break as a result of flexingover an extended period of time. Another quality which must be presentin such artificial leather shoe upper material is abrasion resistancesufficient to be resistant to the relatively minor sending and scrapingto which shoes are so often subjected.

In recent years much attention has been given to solving these problemsand the art pertaining thereto has been advanced. The best type ofsystem found to date has been one which utilizes a fabric substratehaving a surface coating thereon. Thus, both the substrate and thecoating must be air and water vapor permeable to a degree sufiicient tosimulate leather, and the substrate and the coating thereon must besupple and crease-resistant in their composite form to a degreesuflicient to simulate or surpass the properties of natural leather.Additionally, the surface coating must be sculfand abrasion-resistantboth in the wet and in the dry state. One additionally optionalrequirement for the surface coating is that,

where the coating is to have a highly glossy appearance, it should nothave large pores on the surface thereof.

It has generally been found that suitable substrates for syntheticleather type materials can be produced from a batt or fleece ofnon-woven fibrous fabric or from a woven fibrous fabric. The fleece orbatt approach has appeared to take predominance in this area because itsproperties seem to be better suited to this application. Such battingsare generally needled in order to impart resistance to planardelamination thereto and impregnated with a suitable material to renderthe batt relatively dimensionally stable and self-supporting.

It has been proposed to produce porous film-form materials by theso-called coagulation method. In this method, the material from whichthe film will be produced is dissolved in a suitable solvent and thencoagulated from the solvent by the admixture of the solution with asuitable coagulant. For example, French Pat. 822,742 shows the solutionof nitrocellulose in an acetone-alcohol mixture and coagulation of thenitrocellulose into a film-form material by the use of water as acoagulant. In particular, this patent shows the production .of a film bydeposition of the above-described solution on a glass plate andimmersion of the solution-coated glass plate into a water bath. After asuitable immersion time, e.g., about 350 seconds, a coagulated film ofnitrocellulose could be lifted from the glass plate. The patent statesthat coagulation of the film can be accelerated by use of aqueoussolutions of organic acids as the coagulation agent.

It can be appreciated that it is possible to apply a preformed film-formmaterial referred to above to a suitably prepared fibrous or other formsubstrates so as to produce a composite structure having more desirablephysical strength properties than those possessed by the coating filmalone. This has been found to be a less than totally satisfactorysolution to the problem in that additional costs are incurred in joiningthe preformed surface coating to the substrate, and in addition, it hasbeen found that the permeability properties of the composite materialare less advantageous with respect to the instant application use thanare the properties of either the coating or the substrate alone.

It has also been proposed to spray a solution of an elastomeric coatingmaterial directly onto a suitable substrate (cf. US. Pat. 3,109,750).Elastomeric materials which have been suggested for application as topcoatings in this manner are exemplified by polychloroprene,butadiene-styrene, chlorosulfonated polyethylene copolymer,butadiene-acrylonitrile copolymer andvinylidenefluoridehexafluoropropene copolymer. The solvent for theselected elastomer is suitably a mixture of materials wherein theelastomer is soluble in the mixture, but is insoluble in either of thecomponents thereof. For example, mixtures of an alkane and a lowerketone will readily dissolve the elastomer, but the elastomer issubstantially insoluble in either the alkane or the lower ketone chosen.

In this immediately above-referred to process, the solvent componentsare so selected that these have respective vapor pressures, under thesame conditions of temperature and pressure, which are markedlydifferent. The temperature and pressure conditions obtaining duringspraying constitute the most critical conditions at which to determinethe vapor pressure differential of the individual components of thesolvents.

When the elastomer solution is sprayed onto the substrate, the solventcomponent with the higher vapor pressure preferentially evaporatesthereby leaving a mixture of the elastomer and one of the components ofthe solvent (the remaining component being substantially a nonsolventfor the elastomer), wherefrom the elastomer precipitates and coagulatesupon the substrate, whereby a microporous coating is said to beproduced. For example, an elastorneric polymer is dissolved in a solventmixture of acetone and n-hexane (neither acetone nor n-hexane beingindividually a solvent for the chosen elastomer) and the solutionsprayed onto a suitable porous supporting material. When the solution iscoated on the support, one of the components of the solvent (probablyacetone, since it has the lower atmospheric pressure boiling point ofthe two) preferentially evaporates and the elastomer coagulates.

It has been sought to take advantage of the same principle, ofpreferential evaporation of one component of a solvent mixture, inapplying a suitable coating to a substrate by means other than spraying;e.g., brushed on or rolled on coatings. For other purposes it has beensuggested that solutions of cellulose derivatives or vinyl polymers inacetone could be prepared and a precipitant such as toluene for suchpolymers added to such solution in an amount less than that which wouldbe sufficient to cause polymer precipitation. Upon coating of thesolution upon a substrate, the solvent preferentially evaporates,whereby the concentration of the precipitant increases to a levelsufficient to cause coagulation of the dissolved polymer. This techniqueis supposed to result in a porous coating, but tests carried out toconfirm this have shown that the resulting coating is a substantiallyopaque film of individually coagulated or precipitated polymerparticles, where the coating has a thickness great enough to bedesirable for synthetic leather applications.

It was even attempted to produce usable permeable coatings by utilizingelastorneric polymers, such as polychloroprene, butadiene copolymers,acrylic ester polymers and copolymers, polyurethane, in the coatingsolution, but it was found not possible to produce permeable coatingfrom even these polymers, according to this technique, in thicknessgreater than about 0.1 to 0.15 millimeters. Thus, it is apparent thatthese prior art processes do not adequately solve the problem ofproducing an artificial leather material which has sufficient air andwater vapor permeability to be completely acceptable.

In German Pat. 888,706, a process is described by means of whichpermeable coatings are said to be provided on various substratesincluding paper, leather and non-woven battings. According to thisprocess, solutions of a polyurethane polymer in a suitable solvent,e.g., dimethylformamide, are applied to the surface of or impregnatedinto a suitable substrate. The substrate having the suitably appliedpolymer solution is dipped into water to coagulate the polymer and thusprovide a coating on or an impregnant in, as the case may be, thesubstrate. The solvent is said to be removed by action of the watercoagulant.

Further, it has been shown that the water vapor and air permeability offilm-form or sheeting materials produced by coagulation of solutions ofappropriate polymers, utilizing dimethyl formamide or dimethyl sulfoxidesolvent, can be improved if there are admixed with the polymer solutionsemulsifiers, particularly about 0.3 to percent by weight based upon theweight of the entire solution of emulsifier.

Despite the fact that air and water vapor permeable films and coatingshave been produced according to many, if not all, of the prior artprocesses, it is still desirable to produce such film-forming orsheeting materials either in self-supporting form or applied as acoating or impregnant for a suitable substrate.

It is therefore an object of this invention to provide a polyurethanefilm having an outstanding airand water vapor permeability.

It is another object to provide a novel process of producing suchimproved film-form material.

Other and additional objects of this invention will become apparent froma consideration of this entire specification including the claimsappended hereto.

In accord with and fulfilling these objects, this invention comprises,in one of its broad aspects, the production of polyurethane film havingsuperior air and water vapor permeability characteristics. Thisfilm-form material is produced by coagulation thereof from a solventwhich is a mixture of dimethyl sulfoxide and either tetrahydrofuran,acetone, 1,4-dioxane, methyl ethyl ketone or mixtures thereof.

The instant invention will be better understood from a consideration ofthe following fiow diagram:

Solvent Solvent- Polyurethane Coagulant Solvent Film Removal Mixing dzFormation Permeability data presented herein were obtained by practicingthe Mitton test method which appears in Physikalische Messmethoden fiirLeder, JUP l5, Measurement of Water Vapor Permeability.

It is preferred in the practice of this invention to use a solventmixture containing about 30 to 90 percent by weight dimethyl sulfoxideand about 10 to percent by weight of the other solvent used. While it iswithin the contemplation of the practice of this invention to use as theother solvent, mixtures of the above-named sol vents, it is preferred toutilize a single other solvent in admixture with dimethyl sulfoxide, andit is most particularly preferred to use a solvent mixture composed ofdimethyl sulfoxide and tetrahydrofuran.

The polymer solute (and ultimately, the film-form material) is apolyurethane. It has been found that no remarkable improvements in theairand water-vapor permeability are obtained if one works with otherpolymers.

The coagulating agent can be any of the known materials which alone andin suitably proportional admixture with the solvent composition of thisinvention cause the solute polymer material to coagulate from thesolution. Water is the preferred coagulant. Also useful coagulants arelower alcohols, n-hexane and toluene. Mixtures of these coagulants maybe used.

It will, of course, be understood that a judicious selection of thesystem to be used in this invention must be made taking advantage of thecombination of properties of the selected other solvent, coagulant andpolymer. Thus, the chosen other solvent must, in combination withdimethyl sulfoxide, be a solvent for the particular polymer chosen.Similarly, the coagulant chosen must be related to both the solventsystem and to the chosen polymer, since it must have the capacity, inadmixture with the chosen solvent system, to cause the polymer tocoagulate. Data sufficient to make this choice a matter of routine areknown to those skilled in the art or are straight forwardly determinableby such workers as a routine matter.

Film-form and sheet materials may be prepared according to thisinvention either in self-supporting form or as coatings upon a suitablesubstrate. Production of selfsupporting films may be accomplished bycoating of a smooth surface with a polymer solution according to thisinvention; coagulating the polymer into a film; and then lifting thefilm off the surface. Coatings may be applied to supporting substratewhich is itself porous and to which the coated polymer will adhere so asto thus form a composite article comprising the substrate and thecoating thereon by applying to the substrate surface a polymer solutionaccording to this invention; and suitably coagulating the polymer fromsolution onto the substrate as an adherent layer thereon.

A suitable substrate onto which a polymeric coating according to thisinvention may be applied is a fibrous fabric. This fabric may be woven,knitted or a non-woven fleece or batting. The fabric may be composed ofnatural or synthetic organic or inorganic fibers as desired which areexemplified by cellulosics, polyamides, polyesters, wool, silk, linen,acrylics, etc.

By applying the polyurethane to a suitably chosen substrate from asolution, the solvent of which is a mixture of dimethyl sulfoxide and atleast an other solvent, selected from the group consisting oftetrahydrofuran, 1,4- dioxane, acetone and methyl ethyl ketone, it hasbeen surprisingly found that the polyurethane film produced bycoagulation from this solution are significantly more air and watervapor permeable than are similarly coagulated polymer films derived fromthe same polyurethane in solution in either dimethyl sulfoxide or in thesecond solvent alone. This is particularly true in the case ofcoagulation from the other solvent alone from which solutions polymericfilm-form materials have been coagulated having less than 0.5 mg./cm./hr. water vapor permeability.

Where a polyurethane film has been produced by coagulation of apolyester-polyurethane polymer from a solution thereof in dimethylsulfoxide alone, the film had a water vapor permeability of about 2mg./cm. /hr.; whereas the same polymer coagulated in the same mannerinto a film of the same thickness from a solution of the polymer in 80parts by weight of dimethyl sulfoxide and 20 parts by weight oftetrahydrofuran had a water vapor permeability of 4 mg./ cm. hr.

It is surprising that an increase in the water vapor permeability ofpolyurethane films can be realized from coagulation thereof from asolvent mixture according to this invention, which increase is withrespect to the water vapor permeability of film form materials obtainedby production of such films by coagulation thereof from either of thesolvent components alone.

It is even more surprising that a corresponding increase in the watervapor permeability of film-form materials coagulated from dimethylformamide containing combination solvents does not take place. In fact,the water vapor permeability of such films is not in any way improvedover that obtained by coagulation production of materials from solutionin dimethyl formamide alone.

The film-form materials produced by the practice of this invention canbe post-treated, and/or the polymers from which they are producedpro-treated, in the conventional manner. Thus, dyes or pigments can beincorporated according to the usual processes. The product filmformmaterial can be physically treated and worked in the conventionalmanner, such as, for example, by applying suitable finishes thereto ifdesired, roughened with abrasives or smoothed by polishing or byapplying a suitable top coating thereon, as is known in the art.

The solutions for use in this invention may be prepared in aconventional manner, that is, the solvent mixture can first be made withor without emulsifier therein and the suitably selected polymerdissolved therein. In the alternative, the polymer can be dissolved ineither component and the second component then added thereto.

In either case, or regardless of the solution preparation means, it isdesirable that the solution contain no air bubbles trapped therein atthe time of use. In order to insure this condition, the solution issuitably deaerated either by applying a low vacuum over said solution orby merely permitting the solution to stand for a relatively long timebetween preparation and use thereof.

The term film-form material as used herein is intended to encompass bothmaterial coated upon a suitable substrate as well as self-supportingmaterial, as the case may be.

The following examples are given by way of illustration of thisinvention and are in no Way limiting upon the scope thereof. All partsand percentages are by weight, unless expressly stated to be to thecontrary.

EXAMPLE I A ZO-percent solution of a soluble polyester-polyurethane(Estane X7 of Goodrich) was prepared by dissolving such polymer in amixture of parts dimethyl sulfoxide and 20 parts tetrahydrofuran. Thesolution was applied in one coat to a batting of polyamide fiberscontaining butadiene-acrylonitrile copolymer as binding agent (thebatting having a thickness of about 1.2 mm. and a specific gravity ofabout 0.5).

The solution was applied in a thickness of about 1.2 mm. (space betweenrollers). The batting thus coated was immediately placed in water forcoagulation, freed of solvent by rinsing with water (rinsing time about2 hours) and then dried.

After drying, an opaque, white coating was obtained. The water vaporpermeability of the sample thus obtained was about 4 mg./cm. /hr. Thecoating remained undamaged after 200,000 flexings on the BallyFlexometer.

EXAMPLE II A solution of the same polymer as in Example I was preparedin a mixture of 70 parts dimethyl sulfoxide and 30 parts acetone. Thissolution was utilized to produce a coated batting by the same process asdescribed in Example I, and a coated batting was obtained which had awater vapor permeability of about 4 mg./cm. /hr.

EXAMPLE III A solution of a soluble polyester-polyurethane (GoodrichEstane X7) was prepared in a mixture of 60 parts dimethyl sulfoxide and40 parts 1,4-dioxane as the solvent composition in the same manner as inExample I.

A coating on a batting was provided by coagulation of the polymerthereon from said solution, as described in Example I. The coating thusobtained in this manner showed a water vapor permeability of about 5.5to 6 mg./cm. /hr.

EXAMPLE IV A solution of polyurethane was prepared in the same manner asdescribed in Example I, using a mixture of 40 parts dimethyl sulfoxideand 60 parts of methyl ethyl ketone as the solvent. The procedurecontinued as described in Example I. The film-forming material thusobtained had a water vapor permeability between 6.5 and 7 mg./cm. /hr.

Data taken from various tests performed on a variety of coatedsubstrates prepared according to this invention are shown graphically inthe drawing. The film-form material tested was the same as described inExample I, as was the substrate to which it was applied. The curve inthe attached drawing shows data taken from tests conducted on mixedsolvent coagulation produced materials.

What is claimed is:

1. A process for the production of air and water vapor permeablepolyurethane films which comprises dissolving a polyurethane in asolvent composed of a mixture of dimethyl sulfoxide and at least onemember selected from the group consisting of up to 40% tetrahydrofuran,1,4- dioxane, methyl ethyl ketone and acetone; adding a coagulant;coagulating said polyurethane in film-form from said solution; andremoving the solvent from contact with said film-form material.

2. A process as claimed in claim 1, wherein said coagulant is selectedfrom the group consisting of lower alcohols, n-hexane, toluene, waterand mixtures thereof.

3. A process as claimed in claim 1, wherein said filmform material isdeposited upon a substrate and forms a coating thereon.

4. A process as claimed in claim 1, wherein said filmform material isself-supporting.

5. A process as claimed in claim 1 wherein said solvent is a mixture ofdimethyl sulfoxide and 1,4 dioxane.

6. The product produced by the process of claim 1.

2,884,336 4/1959 Loshaek et al. 3,190,765 6/1965 Yuan 26449 XR 3,100,7218/1963 Holden. 3,348,963 10/1967 Fukushima et al. 3,388,100 6/1968 Thomaet al.

FOREIGN PATENTS 639,553 4/1962 Canada.

1,296,758 5/1962 France.

PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R.

